This article is about producing a digital photograph of art work with corrected color and proportions using Adobe Photoshop.
For a good description of the process of photographing art using traditional film look here. I will assume you are using a digital camera, but you could as well be working from a scan from a print or slide.
Set your camera on its highest quality setting. You can reduce the size later if your ultimate presentation will be on a computer monitor.
To greatly facilitate the process of correcting the color we will want three reference colors: true white, true black and true grey.If your art has an area of pure white or pure black in it, you will be able to use those areas. If there is no pure white or pure black in the piece, put a white and/or black card next to it. For the grey, the ideal is a photographic "grey card", available at camera stores. Be sure the grey has no color in it.
If your camera has a zoom lens (which it probably does), select a focal length near the middle of the zoom range in order to avoid unwanted curvature in the image. (Zoom lenses typically produce convex curvature, called barrel distortion, when zoomed out, and concave curvature, called pincushion distortion, when zoomed in.)
If
your work is too large for a copy stand, or you don't have one available, natural
light, outdoors, is your best bet. But make sure the light is even. If your
art has a flat, smooth finish, such as a watercolor or drawing, positioning
the piece perpandicular to the sun, so that your body very nearly (but not quite)
throws a shadow on the picece may work. If you have a great deal of texture
or gloss, as with most oil pieces, be very alert for glare.
Really, the things that are most important in taking the picture are that the light is even, there is no distortion, and there is no glare. Uneven light and distortion are very difficult to correct, and glare is often impossible. But the less you have to change later, the higher your quality will be. So try to get your color accurate and try to get your camera close to perpendicular to your piece.
Here's my photograph. As you see, the color is terrible. (That was intensional.) Also notice that I didn't have the camera directly over the picture. We will correct both of these problems in Photoshop.
Color Correction
First we're going to correct the color. We'll do that very scientifically, since we have the handy white, grey, and black reference areas.
In
Photoshop, select the Color Sampler tool (hiding under the eyedropper tool near
the bottom right side of the toolbox). If your Info Palette is not open, open
it (Menu->Window->Info). Click on the white card in your photograph. Your
Info Palette now has a set of numbers identified as #1. Click on the grey card,
and the Info Palette adds a #2. Then click on the black card to get #3. The
second illustration here shows you what that looked like on my sample picture.
Don't be intimidated by all the numbers. The numbers for each reference point indicate the amount of red (R), green (G), and blue (B) in that point. What you're going to do is balance them all. Since there is an equal amount of each color in white, true grey, and black, balancing the colors in those reference points will correct the color for the photograph. We're also going to make the white card truly white and the black card truly black. That will give us the desired contrast. Are you excited?
I like to make a copy of my image layer and work on the copy, but that's me. If you know how to do that, go ahead. If you don't, that's ok.
Open the Levels Adjustment (Menu->Image->Adjustments->Levels).
Move the Levels dialog somewhere where you will be able to see your Info dialog
and at least some of your photograph. 
The
third illustration here shows the Levels dialog.
Look at your Info dialog. Notice that each of your point samples now has two numbers next to each color letter. The numbers are the same, like "197/197".
Go back to the Levels dialog. At the top of the dialog is a drop-box labeled "Channel". In that window, select "Red". Now, do you see the three triangular sliders under the histogram? (The histogram is the bar-graph that occupies most of the dialog.) The slider on the left is black, the one in the center is grey, and the one on the right is white.
Slide the white slider to the left and look at the numbers in the Info Palette next to "R" for sample #1. Remember, you're adjusting the Red Channel, and you're adjusting the white level. Sample #1 is your white card. The right number of the pair moves as you slide the slider.
In Photoshop, white has a value of 255. Slide the slider until the right number (next to "R" in #1) reads 255.
In Photoshop, black has a value of 0. Slide the black slider to the right until the "R" in sample #3 reads 0. Note that it will not go into negative numbers, so move it just until you get to 0, and no further.
If
your grey card is a photographic grey card, it is exactly "middle grey".
If it's just a random grey, it may be lighter or darker than that. If it's "middle
grey", you want to put the number next to "R" in Sample #2 exactly
half way between 0 and 255, or 127. (It can be very difficult to get the number
exactly where you want. Within one or two of your target is fine.)
You have now adjusted the Red Channel. In the "Channels" drop box, select "Green" and repeat the process, aligning the numbers in the Info Palette next to "G". Then do the same with blue.
Sometimes, as you change one value another will shift. For example, when you change grey, your white may move. Make sure that you end up where you want to be.
The fourth image here is my photo after color correction.
Correcting Proportions
Next we're going to correct the proportions. We'll do this in two steps, even though that will degrade the quality of the image a bit. There is a way to do it in one step, but it's much more complicated to explain.
Select
the Crop Tool from the Tool Box. (It's the third tool down on the left side.)
On the Tool Options Bar (below the Menu Bar) there is a check box labeled "Perspective".
Check that. Now click and drag a rectangle over your photo. It does not have
to be very accurate 
initially.
Then click on a corner point and drag it exactly to the corner of your piece.
Repeat this for the other three corners, then press Enter (Mac: Return). If
you don't get the cropping quite right, click Edit->Undo and try again.
If
you managed to place your art exactly perpendicular to the camera when you took
the picture, you're finished. I, however, had my camera at an angle to the piece,
so my proportions are off. If you have this situation, you need to know the
dimensions of your piece before continuing. (Go get the measurements. I'll wait.)
Now open the Image Size dialog (Menu->Image->Image Size). You may have some pretty odd numbers showing. (I'm not going to go into image size and resolution in this article, so you may just have to trust me on some of this.) Take a look at the check boxes near the bottom of the dialog. If the box labeled "Resample Image" is checked, uncheck it. Chances are your photo represents your piece as too wide for its height. In the "Height" window, type the actual height of your art, then click "OK". Now, open the Image Size dialog again. This time, check the "Resample Image" box then uncheck the "Constrain Proportions" box. Then type the actual width of the piece in the "Width" window. Click "OK".
Now save your finished photograph. I recommend doing a "Save As" rather than overwriting the original photo. That way, if you discover a better way of correcting it, you still have the original to work with.
I hope this has been helpful, and best of luck with your digital portfolio!
RL Geyer
